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Making an Old Trailer Jetter New

08-14-2011, 01:48 AM

Well I own a Spartan 777 trailer jetter. It is running at 1700 PSI @ 16 GPM I talked to the guys at Giant pumps I can upgrade my pump to do a higher PSI at a slightly lower GPM by just changing the manifold head with the plungers and valves. The cost is a few hundred bucks. But I will have to update the motor as well. Here is a link of the series pump I have. The model I am running now is the MP 4130 the kit I would get will be 4124W which can provide me 2500 PSI @ 12 GPM http://www.giantpumps.com/applicatio...manuals/MP.pdf

The motor on my jetter now is a Kohler Magnum 20HP which after talking to Plumber Rick I will have to get a 28HP motor at least. I have 500' of 1/2" hose on the real, just need to change out nozzles. So just wondering on what you all think.

I think since you already have the trailer and reels, that a nice upgrade would be change the motor, and buy a pump that does 3000 psi. Or do the pump upgrade for now and buy the newer complete pump later.

I think since you already have the trailer and reels, that a nice upgrade would be change the motor, and buy a pump that does 3000 psi. Or do the pump upgrade for now and buy the newer complete pump later.

They have a 3000 PSI option but the flow gets a bit less. I was originally looking to buy a new trailer jetter, but the prices are a bit out of my reach right now. So I figured like you said Got the trailer, tank reels and all the plumbing, just need to upgrade the motor and pump. There is plenty of room under the hood for a larger motor, so that will not be an issue. I only paid $2000 for this jetter a few years back. Just had to put a new hose on it, so spending a few more bucks to get more PSI out of it is a lot cheaper than a new unit in my eyes.

Right now the current motor on there needs a good muffler, I was going to make one myself out of black pipe. The reason behind this was not to save a few bucks but to make one that will not blow apart at the seems when the engine backfires. After a few people on Facebook and Plumber Rick told me I should just put a cheap muffler back on. The way they (Spartan), had it is there is a manifold that takes the two cylinders into one, then a triangle three screw bracket to a muffler. So the muffler was only 1 foot away from the engine. I am thinking of having a shop weld a down pipe with a bend that towards the back of the trailer with a couple feet of pipe then attach the muffler and secure it with some hangers off the trailer frame. This way the muffler will be at least 3 feet away from the engine and the backfire will not be as strong when it reaches the muffler.

Comment

Why does the engine back fire? Too high of rpm's when it is shut down? Running rich? Can you drill a hole and run the muffler out the top like a trailer air compressor? And with a 28 hp motor you should still get 12 GPM at 3000 psi maybe more?

Why does the engine back fire? Too high of rpm's when it is shut down? Running rich? Can you drill a hole and run the muffler out the top like a trailer air compressor? And with a 28 hp motor you should still get 12 GPM at 3000 psi maybe more?

This unit has lots of hours on it. I think it might be carbin build up on the head. I have the fuel mixture dailed in. I always make sure I put it in low idle when I turn it off. According to the formula to figure out HP needed for the pump 12 GPM @ 3000 PSI I would need an engine that puts out 35 HP The 28 HP will give me the 2500 PSI @ 12 GPM though.

Comment

if more flow at a given pressure, more power required to do it. likewise for more pressure at a given flow.

in your example, yes, if both engines are turning the pump at 1000 rpm and that makes 10 gpm and there is 1000 psi of resistance to that flow, they are both doing the same thing. but as you start increasing the flow or the pressure requirements, the 10hp engine will get overloaded and bog down and not be able to do it before the 20hp engine.

This is my reminder to myself that no good will ever come from discussing politics or religion with anyone, ever.

The PDF I provided for my pump gives HP for electric motors and the formula for an electric motor. Rick caught that when I was talking to him on the phone. Its HP=(PSI x GPM) / 1440 which will give you eclectic motor HP, to get the HP need by a gas engine its HP=(PSI x GPM) / 1100 Then there is the issue of having the pulleys set to the right size on the motor and pump to get the proper operating RPM.

Comment

The PDF I provided for my pump gives HP for electric motors and the formula for an electric motor. Rick caught that when I was talking to him on the phone. Its HP=(PSI x GPM) / 1440 which will give you eclectic motor HP, to get the HP need by a gas engine its HP=(PSI x GPM) / 1100 Then there is the issue of having the pulleys set to the right size on the motor and pump to get the proper operating RPM.

Thanks Ron. Where do the numbers 1440 and 1100 come from? What's behind them if you know what I mean?

Comment

These are just engine/motor horsepower capacity formulas. Torque is also the factor to consider. A gas engine produces peak hp & torque at certain & different rpm's. An electric motor produces peak hp & torque instantly upon start-up. This is why an electric motor will be less hp than a gas engine for the same application. The formula gpm x psi / 1100 is the minimum hp requirement, an may require bumping up a couple of hp. Let's say peak hp of a 20hp engine may be 3000 rpm, so running it at 1000 rpm just won't do the job, it may only be producing 15 hp or less.

Comment

I'm almost done building a jetter. It's going to be 11 gpm@3600 psi. The engine is a 38hp and it's going to have to turn at 3600 rpm, which is where it achieves max hp. So for less psi & gpm I'll just throttle it back.

Comment

the 1400 and 1100 numbers are about making the units (gpm,psi,horsepower) that flow, pressure, and power are expressed in work out. I think those numbers are cooked just a little for pump efficiency and for motor efficiency as well, because the theoretical number from converting the units is (I believe) 1714.

its complicated to explain how those numbers arise, but if you are interested, here it is.
1 gpm x 1 psi = 231 cubic inches per minute x 1 psi = 3.85 cubic inces per second x 1 psi = 3.85 inch-pounds per second = .321 ft-lb / second

1 hp = 550 ft-lb/sec, so .321/550 = 1/1714

so 1714 is the theoretical number to make the units work out right

the 1100 for gas vs 1400 for electric reflects the difference in how gas and electric motors are rated. They are guestimates, but you mostly won't go wrong using them. For my location I have to further derate a gas engine because they don't make their rated power at this altitude.

for example, the general j3055 I have is rated at 5.5 gpm at 3000psi. it is gas powered, so we use the 1100 number, and get from the formula that it needs an engine with 5.5 x 3000 / 1100 = 15 hp. It has a 16 hp engine, which bogs down and cannot provide the full specs of the pump at this altitude.

I'm putting together a new one now, which is 5.5 at 4kpsi, and should need 20hp. I'm using a 23hp engine.

Comment

the numbers that are used are published numbers by the different manufactures of the pumps/ jetting equipment.

a diesel engine having the most torque per hp is even a higher factor. more like 1895. according to us jetting. 4000 psi x 18gpm = 72,000 / 1895 = 38 hp + 4hp. to run the hydraulic pump for the reel.

my engine is rated at 49.5 hp at 3000 rpm.

although 1 hp should equal 1 hp. in reality the torque is the factor that must be considered.

remember that the pump will deliver the stated volume at the given pump speed. the higher the speed the higher the volume. of course there is a limit to the speed/ rpm of a pump.

now when you start to put the pump under load by raising the pressure on the discharge side, you also put the engine under load, thus decreasing the rpm as the load on the pump goes up.

a gas engine has the least torque per hp while a diesel has the highest.

just think of pulling a heavily loaded trailer such as a semi truck and trailer. diesel is the choice due to the power/ torque of the engine.

so when sizing jetting pumps, make sure to look up the required hp and verify if it's listed as electric or gas. diesel then can be computed based on the formula.

having too little hp will cause the engine to struggle and the pump to run slower. so either the gpm will drop on the lower rpm's or you drop the psi to allow for the rated gpm's and sacrifice the psi.

most pumps will have a graph with a pressure/ gpm curve that shows the required hp for those figures.